there are commercial machines that use a liquid photopolymer and a laser. You can scan a 3d object or feed in a autocad drawing. The object is then "built" from the bottom up 4 thousands of an inch at a time. You can create up to a final object size of a cubic foot with one machine I have seen. Its really cool to watch it make a part. The photopolymer is around $5 an ounce though (I seem to recall).